Image capturing device and auto-focus method thereof

ABSTRACT

An image capturing device includes a lens unit, an image sensor, a face recognition unit, a selecting unit, an auto-focusing (AF) unit and a driving unit. The lens unit focuses images onto the image sensor. The image sensor converts the images into electronic signals. The face recognition unit locates any faces in a current image. If faces are detected, the selecting unit indicates to a user where the faces are located in the image, and selects one of the locations as a main focus area in response to a user input. The driving unit is configured for moving the lens unit. The AF unit controls the driving unit to focus the lens unit according to the selected location.

BACKGROUND

1. Technical Field

The present invention relates to image capturing devices, andparticularly, to an image capturing device and an auto-focus methodthereof.

2. Description of the Related Art

Image capturing devices, such as those used in digital cameras andmobile phones, have an auto-focus (AF) feature. An AF method using facerecognition technology is a relatively new technology. This AF methodenables image capturing devices to automatically detect where a face ofa person is located in a captured image, and adjust the lens to focus onthat face accordingly. However, if more than one face is in view, the AFmethod may not be smart enough to judge which face in the image shouldbe used for focusing.

What is needed, therefore, is an image capturing device that canovercome the above-described problem.

SUMMARY

In a present embodiment, an image capturing device includes a lens unit,an image sensor, a face recognition unit, a selecting unit, anauto-focusing (AF) unit and a driving unit. The lens unit forms imagesonto the image sensor. The image sensor converts the images intoelectronic signals. The face recognition unit locates any faces in acurrent image. If faces are detected, the selecting unit indicates to auser where the faces are located in the image, and selects one of thelocations as a main focus area in response to a user input. The drivingunit is configured for moving the lens unit. The AF unit controls thedriving unit to focus the lens unit according to the selected location.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the present image capturing device and auto-focus methodcan be better understood with reference to the accompanying drawings.The components in the drawings are not necessarily drawn to scale, theemphasis instead being placed upon clearly illustrating the principlesof the present image capturing device and the auto-focus method.Moreover, in the drawings, like reference numerals designatecorresponding parts throughout the several views.

FIG. 1 is a function block diagram of the hardware structure of an imagecapturing device in accordance with a present embodiment.

FIG. 2 is a schematic view showing focus areas of an image displayed bythe image capturing device of FIG. 1.

FIG. 3 is a flowchart of an auto-focus method for an image capturingdevice according to a present embodiment.

DETAILED DESCRIPTION

Embodiments of the present image capturing device and auto-focus methodwill be now described in detail with reference to the drawings. In thefollowing described embodiments, the image capturing device can be butis not limited to a digital still camera, a digital video camera, or anyother electronic device equipped with a camera module.

Referring to FIG. 1, an image capturing device 100, according to anembodiment, includes a lens unit 11, an image sensor 12, a facerecognition unit 13, a selecting unit 14, a memory 15, an auto-focusing(AF) unit 16, and a driving unit 17. The lens unit 11 focuses opticalimages on the image sensor 12. The image sensor 12 converts the opticalimages into electronic signals. During AF, an initial image is capturedand is examined by the face recognition unit 13, which locates any facesin the image. The selecting unit 14 displays the locations on a displayof the image capturing device 100, and selects one of the locations as amain focus area in response to a user input. Then, a number of imagesare captured in quick succession, one for each of a plurality ofpre-determined focus positions of the lens unit 11 as set by the drivingunit 17 under control of the AF unit 16.

The lens unit 11 may include one or many lenses. The lens unit 11 canbe, for example a zoom lens, a macro lens etc.

The image sensor 12 can be a charge coupled device (CCD) image sensor ora complementary metal oxide semiconductor (CMOS) image sensor. Ceramicleaded chip carrier (CLCC) package, a plastic leaded chip carrier(PLCC), or a chip scale package (CSP) may be used for packaging theimage sensor 12.

In this embodiment the face recognition unit 13 is configured forlocating any faces in the initial image then causing those faces to beframed in the image when it is displayed. The face recognition unit 13may be realized by any existing face recognition method.

The selecting unit 14 is configured for displaying the locations on adisplay of the image capturing device 100, and selecting one of thelocations as a main focus area in response to a user input. Theselecting unit 14 shows the image with framed locations of face thereonand sets focus power for determining which location(s) need to be givengreater priority in response to a user input. In this embodiment, theselecting unit 14 is a LCD touch screen. For example, if a framedlocation is touched, the focus power of this touched location is higherthan those of other portions. In addition, the selecting unit 14 canalso be used as a viewfinder of the image capturing device 100.

Users can also set focus powers of framed locations as primary focusarea and subordinate focus areas. For example, the users can touchseveral framed locations, and the degrees of emphasis can be determinedunder the control of the duration of touch on the corresponding framedlocations. Referring to FIG. 2, this shows an image of two persons: afirst person 111 and a second person 112. A user may want to giveemphasis to the area of the second person 112 as a primary photo object,and the first person 111 as a subordinate photo object. In order to dothis, the selecting unit 14 is used to set focus powers for the portionof the first person 111 and the portion of the second person 112. Afocus power for the non-focus areas of the current image besides theselected focus areas can also be set. In the illustrated example, thevalue of the focus power for the face of the second person 112 is set as5, assuming the values of focus power range from 0 to 5. The value ofthe focus power of the face of the first person 111 is set as 3, and thevalue of the focus power of the non-emphasized areas is set as 1. It isto be understood that the focus power of the non-emphasized areas of thecurrent image can instead be set at predetermined default value, such as0.

The image capturing device 100 further comprises a memory 15 configuredfor storing the area of the image containing the highlighted face (mainfocus area) selected by the selecting unit 14 according to the user'sinput, and focus powers corresponding to the highlighted face and focuspowers corresponding to other areas besides the highlighted face.

The AF unit 16 can focus the lens unit 11 with emphasis on any portionof the image. In this embodiment, the AF unit 16 receives the focuspowers and thereby focuses on locations accordingly. In detail, variousmethods, such as a contrast measurement method, can be used by the unit.

The AF unit 16 can receive information regarding the selected main focusarea and the non-emphasized focus areas and corresponding focus powersof the main focus area and the non-focus areas from the memory 15. TheAF unit 16 calculates a base evaluation value of an image of the currentimage. This is obtained by taking the total of multiplying a baseevaluation value of each main focus area and non-focus area by the focuspower corresponding to the area. Then the AF unit 16 gets a maximalevaluation value of these photographing images and the position of thelens unit 11 corresponding to the maximal evaluation value named asin-focus position (main focus position). The base evaluation value ofeach area can be contrast, grayscale, or intensity of the area. The AFunit 16 can control the auto-focus operation of the image capturingdevice 100 to detect an in-focus position of the lens unit 11 basingupon the base evaluation value. The method of detecting the in-focusposition of the lens unit 11 can be any of various kinds of knownmethods, such as a hill-climbing method. The AF unit 16 controls thedriving unit 17 to move the lens unit 11 to the in-focus position basedupon the position of the lens unit 11 corresponding to the maximalevaluation value.

The driving unit 17 is configured for moving the lens unit 11 back andforth under control of the AF unit 16. The driving unit 17 moves thelens unit 11 during the process of detecting the in-focus position ofthe lens unit 11, and moves the lens unit 11 to the in-focus positiononce the in-focus position of the lens unit 11 has been detected.

Referring to FIG. 3, a flowchart of an auto-focus method for the imagecapturing device 100 is shown. The method includes the steps of: framingfaces in a current image; selecting one face as main focus area, andsetting focus powers for the main focus area and non-focus areas of thecurrent images; storing the focus areas and focus powers correspondingto the focus area and focus powers corresponding to the non-focus areas;performing an auto-focus process using a base evaluation value of animage of the current image, wherein the base evaluation value iscalculated by taking the total of multiplying a base evaluation value ofeach focus area and non-focus areas by the focus power corresponding tothe focus areas and non-focus area; and moving a lens unit 11 of theimage capturing device 100 to an in-focus position.

It will be understood that the above particular embodiments and methodsare shown and described by way of illustration only. The principles andthe features of the present invention may be employed in various andnumerous embodiment thereof without departing from the scope of theinvention as claimed. The above-described embodiments illustrate thescope of the invention but do not restrict the scope of the invention.

1. An image capturing device comprising: an image sensor; a lens unitconfigured for focusing images onto an image sensor; a face recognitionunit configured for detecting a number of locations where the faces ofthe persons are located in a current image; a selecting unit configuredfor displaying where the faces are located in the image and selectingone of the locations as a main focus area in response to a user input; adriving unit configured for moving the lens unit; and an AF unitconfigured for calculating a in-focus position and controlling thedriving unit to focus the lens unit according to the in-focus position.2. The image capturing device as claimed in claim 1, wherein theselecting unit comprises a touch screen which is used for selecting alocation as main focus area on the touch screen.
 3. The image capturingdevice as claimed in claim 1, wherein the image capturing device is adevice selected from the group consisting of a digital camera, a videocamera and a mobile phone.
 4. The image capturing device as claimed inclaim 1, wherein the image sensor is a charge-coupled device or acomplementary metal oxide semiconductor device.
 5. The image capturingdevice as claimed in claim 1, wherein the image sensor is one selectedfrom the group consisting of a ceramic leaded chip carrier package typeimage sensor, a plastic leaded chip carrier package type image sensorand a chip scale package type image sensor.
 6. An image capturing devicecomprising: an image sensor; a lens unit configured for focusing imagesonto an image sensor; a face recognition unit configured for detecting anumber of locations where the faces of the persons are located in acurrent image; a selecting unit configured for displaying where thefaces are located in the image and selecting one of the locations as amain focus area in response to a user input; a memory configured forstoring the main focus area selected by the selecting unit and focuspowers corresponding to the main focus area, and focus powerscorresponding to other areas besides the main focus area of the currentimage; a driving unit configured for moving the lens unit; and an AFunit is configured for calculating a in-focus position and controllingthe driving unit to focus the lens unit according to the in-focusposition.
 7. The image capturing device as claimed in claim 6, whereinthe image capturing device is a device selected from the groupconsisting of a digital camera, a video camera and a mobile phone. 8.The image capturing device as claimed in claim 6, wherein the imagesensor is a charge-coupled device or a complementary metal oxidesemiconductor device.
 9. The image capturing device as claimed in claim6, wherein the image sensor is one selected from the group consisting ofa ceramic leaded chip carrier package type image sensor, a plasticleaded chip carrier package type image sensor and a chip scale packagetype image sensor.
 10. The image capturing device as claimed in claim 6,wherein the focus power of the areas of the image besides the main focusarea is a predetermined default value.
 11. The image capturing device asclaimed in claim 10, wherein the predetermined default value is
 0. 12.An auto-focus method for an image capturing device, the methodcomprising: framing faces in a current image; selecting one face as mainfocus area, and setting focus powers for the focus area and non-focusareas of the current images; storing the focus areas and focus powerscorresponding to the focus area and focus powers corresponding to thenon-focus areas; performing an auto-focus process using a baseevaluation value of an current image, wherein the base evaluation valueis calculated by taking the total of multiplying a base evaluation valueof each focus area and non-focus area by the focus power correspondingto the focus areas and non-focus area; and moving a lens unit of theimage capturing device to an in-focus position.
 13. The method asclaimed in claim 12, wherein the evaluation value of current image isone selected from the group consisting of contrast, grayscale andintensity.
 14. The method as claimed in claim 12, wherein the focuspower of the areas besides the main focus area is a predetermineddefault value.
 15. The method as claimed in claim 12, wherein the imagecapturing device is a device selected from the group consisting of adigital camera, a video camera and a mobile phone.
 16. The method asclaimed in claim 14, wherein the predetermined default value is 0.